U.S. patent number 6,768,427 [Application Number 10/396,561] was granted by the patent office on 2004-07-27 for encoder initialization methods and related systems.
This patent grant is currently assigned to Lexmark International, Inc.. Invention is credited to Christopher A. Adkins, Michael A. Marra, III, Jay W. Vessels, John T. Writt.
United States Patent |
6,768,427 |
Adkins , et al. |
July 27, 2004 |
Encoder initialization methods and related systems
Abstract
In one aspect, in a device such as a printer, an encoder system
method initializes the system to produce analog output signals that
fall outside the detection range of an A/D converter of the system.
In another aspect, in a device such as a printer, an encoder system
method initializes the system without converting analog signal
levels into corresponding digital values.
Inventors: |
Adkins; Christopher A.
(Lexington, KY), Marra, III; Michael A. (Lexington, KY),
Vessels; Jay W. (Lexington, KY), Writt; John T.
(Lexington, KY) |
Assignee: |
Lexmark International, Inc.
(Lexington, KY)
|
Family
ID: |
32712902 |
Appl.
No.: |
10/396,561 |
Filed: |
March 25, 2003 |
Current U.S.
Class: |
341/13;
341/16 |
Current CPC
Class: |
G01D
5/347 (20130101) |
Current International
Class: |
G01D
5/347 (20060101); G01D 5/26 (20060101); H03M
001/22 () |
Field of
Search: |
;341/13,16,118,120,155
;250/233,231.16,205,214,233.16,204
;347/248,250,214R,206.1,234,235 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
60140118 |
|
Mar 1985 |
|
JP |
|
WO 00/25167 |
|
May 2000 |
|
WO |
|
Primary Examiner: Tokar; Michael
Assistant Examiner: Nguyen; Linh Van
Attorney, Agent or Firm: Thompson Hine LLP
Claims
What is claimed is:
1. A method for initializing an encoder system that provides a
varying analog output signal to an analog signal detector having a
detection range defined by a maximum and a minimum, the encoder
system including at least one component that can be controlled to
vary at least a peak to peak amplitude of the analog output signal,
the method comprising the steps of: (a) measuring an output of the
analog signal detector while the component is at a first setting;
(b) measuring the output of the analog signal detector while the
component is at a second setting; (c) based at least in part upon
measurements made in steps (a) and (b), defining an operating
setting for the component so as to place an upper envelope of the
analog output signal above the maximum of the detection range and a
lower envelope of the analog output signal below the minimum of the
detection range when the encoder system operates with the component
at the operating setting.
2. The method of claim 1 wherein the operating setting is defined
to place the upper envelope higher than the maximum of the
detection range by at least a certain amount and the lower envelope
below the minimum of the detection range by at least the certain
amount.
3. The method of claim 2 wherein the certain amount is about five
percent of the amplitude defined by the maximum minus the
minimum.
4. The method of claim 1 wherein the encoder provides first and
second analog output signals, and steps (a), (b) and (c) are
carried out for each of the first and second analog output
signals.
5. The method of claim 4 wherein the at least one component
comprises a light element, a first offset component to vary a
mid-point of the first analog output signal and a second offset
component to vary a mid-point of the second analog output signal,
further comprising the step of centering both the first and second
analog output signals about the detection range.
6. The method of claim 4 wherein the operating setting is defined
to place an upper crossover of the first and second analog output
signals within the detection range and place a lower crossover of
the first and second analog encoder output signals within the
detection range.
7. The method of claim 6 wherein the upper crossover is placed near
the maximum of the detection range and the lower crossover is
placed near the minimum of the detection range.
8. The method of claim 1 wherein the at least one component
comprises both a light element with an adjustable energization
level and DC offset circuitry associated with a photo sensor,
wherein: step (a) is performed while the light element is energized
at a first energization level and the DC offset circuitry is set at
a first offset level; step (b) is performed while the light element
is energized at a second energization level and the DC offset
circuitry is set at a second offset level; step (c) involves
performing a calculation to define an operating energization level
for the light element and an operating offset level for the DC
offset circuitry, where the operating offset level is further
defined to center the analog output signal about the detection
range.
9. The method of claim 8 wherein the first offset level and the
second offset level are the same.
10. The method of claim 1 wherein the analog signal detector
comprises an analog to digital converter.
11. The method of claim 1 wherein in step (a) the component first
setting maintains the entire analog output signal within the
detection range of the analog signal detector and the maximum
amplitude and minimum amplitude of the analog output signal are
measured, and in step (b) the component second setting also
maintains the entire analog output signal within the detection
range and the maximum amplitude and minimum amplitude of the analog
output signal are measured.
12. A printer, carrying out the method of claim 1, the printer
including a control unit connected to receive the output of the
analog signal detector, the control unit having an output connected
to control the setting of the component, the encoder connected to
track movement of one of a print head carriage and a paper feed
path roller, wherein the control unit effects the steps of claim
1.
13. A method for initializing an encoder system that includes a
movable element and produces at least first and second varying
analog output signals in response to movement of the movable
element, the encoder system including at least one output affecting
component that can be adjusted, the method comprising the steps of:
(a) inputting the first and second analog output signals to an
analog to digital converter having a detection range defined by a
maximum and a minimum; (b) for each of the first and second analog
output signals, measuring a corresponding output of the analog to
digital converter while the movable encoder element is moving and
the output affecting component is set at at least one known
setting; (c) based at least in part upon the measuring done in step
(b), defining an operating setting for the output affecting
component so as to place an upper envelope of each of the first and
second analog output signals above the maximum of the detection
range and the lower envelope of each of the first and second analog
output signals below the minimum of the detection range.
14. The method of claim 13 wherein the at least one output
affecting component comprises a light element, dc offset circuitry
associated with the first analog output signal and dc offset
circuitry associated with the second analog output signal.
15. The method of claim 14 wherein in step (c) an operating
energization level of the light element is defined.
16. The method of claim 15 wherein in step (c) an operating offset
setting for the dc offset circuitry associated with both of the
first and second analog output signals is defined so as to center
both of the first and second analog output signals about the
detection range.
17. The method of claim 13 wherein step (b) is performed for at
least first and second known settings of the output affecting
component.
18. The method of claim 17 wherein both the first and second known
settings maintain both the first and second analog output signals
entirely within the detection range.
19. The method of claim 17 wherein the first and second known
settings maintain both an upper crossover and a lower crossover of
the first and second analog output signals within the detection
range, and step (c) involves using determined signal crossover
levels of the analog output signals at both the first and second
known settings to define the operating settings.
20. A printer, comprising: an encoder system for providing a
varying analog output signal in response to movement of a moveable
part of the printer, the encoder system including at least one
component that can be controlled to vary at least a peak to peak
amplitude of the analog output signal; an analog signal detector
having a set detection range defined by a maximum and a minimum,
the analog signal detector receiving the analog output signal; a
control unit connected to control movement of the moveable part of
the printer and to control a setting of the component, the control
unit receiving a digital output of the analog signal detector, the
control unit having at least an encoder initialization mode in
which it effects the following steps: (a) measuring an output of
the analog signal detector while the component is at a first
setting and the moveable part of the printer is moving; (b)
measuring the output of the analog signal detector while the
component is at a second setting and the moveable part of the
printer is moving; (c) based at least in part upon measurements
made in steps (a) and (b), defining an operating setting for the
component so as to place an upper envelope of the analog output
signal above the maximum of the detection range and a lower
envelope of the analog output signal below the minimum of the
detection range when the encoder operates with the encoder
component at the operating setting.
21. The printer of claim 20 wherein the encoder provides first and
second analog output signals to the analog signal detector, and the
control unit effects steps (a), (b) and (c) for each of the first
and second analog output signals.
22. The printer of claim 21 wherein the at least one component
comprises a light element with an adjustable energization level and
a photo sensor and DC offset circuitry combination for each analog
output signal, and in step (c) the control unit defines an
operating energization level for the photo sensor and also defines
operating settings of the DC offset circuitry so as to center both
the first and second analog output signals about the detection
range.
23. The printer of claim 20 wherein in step (a) the component first
setting maintains the entire analog output signal within the
detection range of the analog signal detector and the maximum
amplitude and minimum amplitude of the analog output signal are
measured, and in step (b) the component second setting also
maintains the analog output signal within the detection range and
the maximum amplitude and minimum amplitude of the analog output
signal are measured.
24. The printer of claim 20 wherein the control unit initiates the
initialization mode steps in response to detection of an ambient
printer condition.
25. The printer of claim 24 wherein the ambient printer condition
is a temperature condition.
26. The printer of claim 25 wherein the temperature condition is
one of (i) a detected temperature change of at least a certain
amount since last initialization or (ii) a detected temperature
exceeding a predetermined temperature.
27. A method for initializing an encoder system that produces an
analog output signal on an output channel, without converting
analog signal levels of the analog output signal into corresponding
digital values, the system including a light element with an
adjustable energization level and the output channel including a
photo sensor producing a signal as a function of light received and
dc offset circuitry for offsetting the signal to produce the analog
output signal, the method comprising the steps of: (a) inputting
the analog output signal to an upper level detector that detects
when the analog output signal increases to an upper threshold
level; (b) repeatedly adjusting the setting of the dc offset
circuitry to increase the offset of the analog output signal until
the level detector outputs an indicator that the upper threshold
level is reached; (c) recording the setting of the dc offset
circuitry corresponding to output of the indicator of step (b); (d)
inputting the analog output signal to a lower level detector that
detects when the analog output signal decreases to a lower
threshold level; (e) repeatedly adjusting the setting of the dc
offset circuitry to decrease the offset of the analog output signal
until the lower level detector outputs an indicator that the lower
threshold level is reached; (f) recording the setting of the dc
offset circuitry corresponding to output of the indicator of step
(e); (g) placing the setting of the dc offset circuitry at a level
to produce a high dc offset and repeatedly adjusting the
energization level of the light element to increase an envelope of
the analog output signal until the lower level detector outputs an
indicator that the lower threshold level is reached; (h) subsequent
to step (g), adjusting the energization level of the light element
to place the envelope of the analog output signal above the lower
threshold level and: (i) adjusting the setting of the dc offset
circuitry to decrease the offset of the envelope until the level
detector outputs an indicator that the lower threshold level is
reached; (ii) recording the setting of the dc offset circuitry
corresponding to output of the indicator of (h)(i); (i) subsequent
to step (h), placing the setting of the dc offset circuitry at a
level to produce a low dc offset and: (i) adjusting the setting of
the dc offset circuitry to increase the offset of the envelope
until the upper level detector outputs an indicator that the upper
threshold level is reached; (ii) recording the setting of the dc
offset circuitry corresponding to output of the indicator of
(i)(i).
28. The method of claim 27, further comprising: (j) based at least
in part upon the recorded values of steps (c), (f), (h)(ii) and
(i)(ii), calculating an amplitude of the envelope of the analog
output signal.
29. The method of claim 28, further comprising: (k) based at least
in part upon the recorded values of steps (h)(ii) and (i)(ii),
calculating an operating setting of the dc offset circuitry that
will center the envelope of the analog output signal about the
upper threshold level and the lower threshold level.
30. The method of claim 29, further comprising: (l) calculating a
peak to peak amplitude of the analog output signal; (m) if the peak
to peak amplitude of the analog output signal is below a set
threshold, calculating an adjustment energization level for the
light element to increase the peak to peak amplitude of the analog
output signal to at least the set threshold.
31. The method of claim 30, further comprising: (n) subsequent to
step (m), calculating an adjusted operating setting for the dc
offset circuitry to re-center the envelope of the analog output
signal about the upper threshold level and the lower threshold
level.
32. The method of claim 27 wherein the encoder system includes a
moveable element that varies light received by the photo sensor as
the moveable element moves, wherein during all of steps (a) through
(i) the moveable element is moved at a substantially constant
rate.
33. The method of claim 27 wherein the upper level detector and
lower level detector are formed together as a Schmitt trigger
device.
34. The method of claim 33 wherein the Schmitt trigger includes
latching circuitry at its output side.
35. A printer including the encoder system of claim 27 and carrying
out the initialization method of claim 27.
36. A method for initializing an encoder system that produces an
analog output signal on an output channel, without converting
analog signal levels of the analog output signal into corresponding
digital values, the system including a light element with an
adjustable energization level and the output channel including a
photo sensor producing a signal as a function of light received and
dc offset circuitry for offsetting the signal to produce the analog
output signal, the method comprising the steps of: (a) inputting
the analog output signal to at least one level detector that
detects when the analog output signal increases to an upper
threshold level and when the analog output signal decreases to a
lower threshold level; (b) while the energization level of the
light element is set at a first energization level, adjusting the
setting of the dc offset circuitry and monitoring for changes in
output of the level detector to identify a first offset setting
corresponding to the upper threshold level and a second offset
setting corresponding to the lower threshold setting; (c) while the
energization level of the light element is set at a second
energization level, adjusting the setting of the dc offset
circuitry and monitoring for changes in output of the level
detector to identify a third offset setting corresponding to the
upper threshold level and a fourth offset setting corresponding to
the lower threshold setting; (d) based at least in part upon the
first, second, third and fourth offset settings identified in steps
(b) and (c), establishing an operating energization level for the
light element and an operating offset setting for the dc offset
circuitry.
37. The method of claim 36 wherein the first energization level is
substantially zero and wherein the second energization level is
non-zero.
38. The method of claim 36 wherein the encoder system includes a
moveable element that varies light received by the photo sensor as
the moveable element moves, wherein during steps (b) and (c) the
moveable element is moved at a substantially constant rate.
39. The method of claim 36 wherein the at least one level detector
comprises a Schmitt trigger.
40. The method of claim 39 wherein the Schmitt trigger includes
latching circuitry at its output side.
41. The method of claim 36 wherein the at least one level detector
comprises a first level detector for the upper threshold level and
a second level detector for the lower threshold level.
42. A printer including the encoder system of claim 36 and carrying
out the initialization method of claim 36.
43. A method for initializing an encoder system that produces an
analog output signal on an output channel, without converting
analog signal levels of the analog output signal into corresponding
digital values, the system including a light element with an
adjustable energization level and the output channel including a
photo sensor producing a signal as a function of light received and
dc offset circuitry for offsetting the signal to produce the analog
output signal, the method comprising the steps of: (a) inputting
the analog output signal to at least one level detector that
detects when the analog output signal increases to an upper
threshold level and detects when the analog output signal decreases
to a lower threshold level; (b) adjusting the setting of the dc
offset circuitry and monitoring for changes in output of the level
detector to identify offset settings corresponding to the upper
threshold level and the lower threshold level; (c) based at least
in part upon the offset settings identified in step (b),
establishing an operating energization level for the light element
and an operating offset setting for the dc offset circuitry.
44. The method of claim 43 wherein the at least one level detector
comprise a Schmitt trigger.
45. The method of claim 44 wherein the Schmitt trigger includes
latching circuitry at its output side.
46. The method of claim 45 wherein step (b) involves at least: (1)
while the energization level of the light element is set at a first
energization level, adjusting the setting of the dc offset
circuitry and monitoring for changes in output of the Schmitt
trigger to identify offset settings corresponding to the upper
threshold level and the lower threshold level; and (2) while the
energization level of the light element is set at a second
energization level, adjusting the setting of the dc offset
circuitry and monitoring for changes in output of the Schmitt
trigger to identify offset settings corresponding to the upper
threshold level and the lower threshold level.
47. The method of claim 43 wherein the operating energization level
for the light element and the operating offset setting for the dc
offset circuitry are established to center the analog output signal
about the range defined by the upper threshold level and the lower
threshold level, and to place an upper envelope of the analog
output signal above the upper threshold level and a lower envelope
of the analog output signal below the lower threshold level.
48. The method of claim 43, wherein the encoder system produces a
first analog output signal on a first output channel and a second
analog output signal on a second output channel, and each output
channel includes a corresponding photo sensor and corresponding dc
offset circuitry, wherein steps (a), (b) and (c) are performed for
both the first analog output signal and the second analog output
signal.
49. In a printer including an encoder system with a movable element
connected for movement with a printer structure, the encoder system
including at least one light element and at least first and second
output channels, the first output channel producing an analog
output signal that varies according to light received by a first
photo sensor and the second output channel producing an analog
output signal that varies as a function of light received by a
second photo sensor, wherein movement of the movable element varies
light received by the first and second photo sensors, a signal
detection system comprising: a first Schmitt trigger connected to
receive the analog output signal of the first output channel and
having a first upper detection threshold and a first lower
detection threshold, first latching circuitry connected to an
output of the first Schmitt trigger for producing (i) a latched
output corresponding to the analog output signal of the first
output channel reaching the first upper detection threshold and
(ii) a latched output corresponding to the analog output signal of
the first output channel reaching the first lower detection
threshold; and a second Schmitt trigger connected to receive the
analog output signal of the second output channel and having a
second upper detection threshold and a second lower detection
threshold, second latching circuitry connected to an output of the
second Schmitt trigger for producing (i) a latched output
corresponding to the analog output signal of the second output
channel reaching the second upper detection threshold and (ii) a
latched output corresponding to the analog output signal of the
second output channel reaching the second lower detection
threshold.
50. The printer of claim 49 wherein the first upper detection
threshold and the second upper detection threshold are
substantially the same, and the first lower detection threshold and
the second lower detection threshold are substantially the
same.
51. The printer of claim 50 wherein the latched outputs of the
first latching circuitry and the second latching circuitry are
provided as inputs to a control unit that is operable to initialize
the encoder system.
52. The printer of claim 51 wherein the control unit is connected
to reset the first latching circuitry and second latching
circuitry.
53. In a printer including one of a print head carriage and a paper
feed roller connected with an encoder system that produces a
varying analog output signal corresponding to movement of the one
of the carriage and roller, the encoder system including at least
one component that can be controlled to vary the analog output
signal and a control unit operable to initialize the encoder system
to achieve a suitable encoder output signal for use in monitoring
movement of the one of the carriage and the roller, a method of
triggering an initialization process, comprising the steps of:
detecting an ambient temperature condition of the printer, and
triggering the initialization process if the ambient temperature
condition satisfies a certain parameter.
54. The method of claim 53 wherein the certain parameter comprises
one of (i) a detected temperature change of at least a certain
amount since last initialization or (ii) a detected temperature
exceeding a predetermined temperature.
Description
TECHNICAL FIELD
The present invention relates generally to encoders, and more
particularly, to both analog and digital encoder systems and
methods for initializing such systems.
BACKGROUND OF THE INVENTION
The cost of analog encoders increases as the encoder components
such as the encoder mask, light element and photo sensors are made
more precise and/or with higher tolerances. When working with less
expensive encoders the encoder output signals produced have a
tendency to be further removed from ideal signals.
U.S. Pat. No. 6,452,512 describes a desirable encoder system having
an A/D converter, and a related initialization process in which
adjustments to an encoder light element energization level are
made, along with adjustments to a dc offset of the signal, in order
to produce suitable encoder signals that are within a detection
range of the A/D converter.
In one aspect, it would be advantageous to provide an encoder
initialization method which can be used to achieve desired encoder
signals that are saturated beyond the detection range of an A/D
converted or other analog signal detector.
In another aspect, it would be desirable to provide an encoder
system and related initialization method that does not require the
analog signal levels of an encoder signal to be converted into
corresponding digital values, thus saving the cost of an A/D
converter.
SUMMARY OF THE INVENTION
In one aspect, a method is provided for initializing an encoder
system that provides a varying analog output signal to an analog
signal detector having a detection range defined by a maximum and a
minimum, the encoder system including at least one component that
can be controlled to vary at least a peak to peak amplitude of the
analog output signal. The method involves the steps of: (a)
measuring an output of the analog signal detector while the
component is at a first setting; (b) measuring the output of the
analog signal detector while the component is at a second setting;
and (c) based at least in part upon measurements made in steps (a)
and (b), defining an operating setting for the component so as to
place an upper envelope of the analog output signal above the
maximum of the detection range and a lower envelope of the analog
output signal below the minimum of the detection range when the
encoder operates with the component at the operating setting.
In another aspect, a method is provided for initializing an encoder
system that includes a movable element and produces at least first
and second varying analog output signals in response to movement of
the movable element, the encoder system including at least one
output affecting component that can be adjusted. The method
involves the steps of: (a) inputting the first and second analog
output signals to an analog to digital converter having a detection
range defined by a maximum and a minimum; (b) for each of the first
and second analog output signals, measuring a corresponding output
of the analog to digital converter while the movable encoder
element is moving and the output affecting component is set at at
least one known setting; and (c) based at least in part upon the
measuring done in step (b), defining an operating setting for the
output affecting component so as to place an upper envelope of each
of the first and second analog output signals above the maximum of
the detection range and the lower envelope of each of the first and
second analog output signals below the minimum of the detection
range.
In a further aspect, a printer includes the encoder system of the
preceding paragraph, and a control unit that carries out the method
steps of the preceding paragraph.
In yet another aspect, a method is provided for initializing an
encoder system that produces an analog output signal on an output
channel, without converting analog signal levels of the analog
output signal into corresponding digital values, the system
including a light element with an adjustable energization level and
the output channel including a photo sensor producing a signal as a
function of light received and dc offset circuitry for offsetting
the signal to produce the analog output signal. The method involves
the steps of: (a) inputting the analog output signal to at least
one level detector that detects when the analog output signal
increases to an upper threshold level and when the analog output
signal decreases to a lower threshold level; (b) while the
energization level of the light element is set at a first
energization level, adjusting the setting of the de offset
circuitry and monitoring for changes in output of the level
detector to identify a first offset setting corresponding to the
upper threshold level and a second offset setting corresponding to
the lower threshold setting; (c) while the energization level of
the light element is set at a second energization level, adjusting
the setting of the dc offset circuitry and monitoring for changes
in output of the level detector to identify a third offset setting
corresponding to the upper threshold level and a fourth offset
setting corresponding to the lower threshold setting; and (d) based
at least in part upon the first, second, third and fourth offset
settings identified in steps (b) and (c), establishing an operating
energization level for the light element and an operating offset
setting for the dc offset circuitry.
In still a further aspect, a method is provided for initializing an
encoder system that produces an analog output signal on an output
channel, without converting analog signal levels of the analog
output signal into corresponding digital values, the system
including a light element with an adjustable energization level and
the output channel including a photo sensor producing a signal as a
function of light received and dc offset circuitry for offsetting
the signal to produce the analog output signal. The method involves
the steps of: (a) inputting the analog output signal to at least
one level detector that detects when the analog output signal
increases to an upper threshold level and detects when the analog
output signal decreases to a lower threshold level; (b) adjusting
the setting of the dc offset circuitry and monitoring for changes
in output of the level detector to identify offset settings
corresponding to the upper threshold level and the lower threshold
level; and (c) based at least in part upon the offset settings
identified in step (b), establishing an operating energization
level for the light element and an operating offset setting for the
dc offset circuitry.
In another aspect, a printer includes an encoder system with a
movable element connected for movement with a printer structure,
the encoder system including at least one light element and at
least first and second output channels, the first output channel
producing an analog output signal that varies according to light
received by a first photo sensor and the second output channel
producing an analog output signal that varies as a function of
light received by a second photo sensor. Movement of the movable
element varies light received by the first and second photo
sensors. A signal detection system includes a first Schmitt trigger
connected to receive the analog output signal of the first output
channel and having a first upper detection threshold and a first
lower detection threshold, with first latching circuitry connected
to an output of the first Schmitt trigger for producing (i) a
latched output corresponding to the analog output signal of the
first output channel reaching the first upper detection threshold
and (ii) a latched output corresponding to the analog output signal
of the first output channel reaching the first lower detection
threshold. The signal detection system further includes a second
Schmitt trigger connected to receive the analog output signal of
the second output channel and having a second upper detection
threshold and a second lower detection threshold, with second
latching circuitry connected to an output of the second Schmitt
trigger for producing (i) a latched output corresponding to the
analog output signal of the second output channel reaching the
second upper detection threshold and (ii) a latched output
corresponding to the analog output signal of the second output
channel reaching the second lower detection threshold.
In a further aspect, a printer includes one of a print head
carriage and a paper feed roller connected with an encoder system
that produces a varying analog output signal corresponding to
movement of the one of the carnage and roller, the encoder system
including at least one that can be controlled to vary the analog
output signal and a control unit operable to initialize the encoder
system to achieve a suitable encoder output signal for use in
monitoring movement of the one of the carriage and the roller. A
method of triggering an initialization process in the printer
involves the steps of: detecting an ambient temperature condition
of the printer; and triggering the initialization process if the
ambient temperature condition satisfies a certain parameter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of one embodiment of an encoder system of a
printer;
FIG. 2 is a flow chart of one embodiment of an encoder system
initialization process;
FIG. 3 is a graph depicting one encoder output signal during the
process of FIG. 2;
FIG. 4 is a schematic of another embodiment of an encoder system of
a printer;
FIG. 5 is a schematic of latching circuitry of the system of FIG.
5;
FIGS. 6A, 6B, 6C and 6D depict a flow chart of another embodiment
of an encoder initialization process; and
FIG. 7 is a graph depicting one encoder output signal during the
process of FIGS. 6A-6D.
DETAILED DESCRIPTION
Referring to FIG. 1, a schematic of an encoder system 10 is
illustrated and includes an analog encoder 12 having a light
element 14 such as an LED and photo sensors 16 which may take the
form of photo diodes. In the case of a rotary encoder a rotating,
windowed mask may be positioned between the light element 14 and
photo sensors 16. In the case of a linear encoder the light element
14 and photo sensors 16 may move relative to a fixed, windowed
encoder mask strip. A structure 18 such as a rotating printer feed
roller or a reciprocating print head carriage mounted for movement
across a paper path is associated with the encoder 12 as is
commonly known in the art. The encoder 12 includes amplification
and offset circuitry 20 for each of the A and B channels that acts
on the output of the photo sensors 16 to produce the analog A and B
output signals of the encoder, which are provided to a controller
22. In the illustrated embodiment the controller 22 is formed by an
ASIC in combination with firmware or other code. An A/D converter
24 receives the analog A and B signals of the encoder 12. The A/D
converter 24 outputs digital values corresponding to analog levels
of the A and B signals to a min/max detection circuit 26. The
min/max detection circuit 26 outputs minimum and maximum values
(A.sub.MAX, A.sub.MIN, B.sub.MAX, B.sub.MIN) for each of the A and
B signals for analysis or examination by an initialization module
28 which may be formed by firmware code. The initialization module
is associated with a motor control PWM module 30, an encoder
energization PWM module 32, an A channel offset PWM module 34 and a
B channel offset PWM module 36. In each case the initialization
module 28 can adjust a duty cycle that the particular PWM module
uses to produce its output PWM signal. The PWM signal MOTOR_PWM
output by the motor control PWM module 30 is provided to control
the movement of a motor associated with the printer structure 18.
The PWM signal LED_PWM output by the encoder energization PWM
module 32 is provided to a current drive circuit 38 for controlling
the energization level of the encoder light element 14. The PWM
signal OFFSETA_PWM output by the offsetA PWM module 34 controls the
dc offset applied to the signal output by the photo sensor
associated with the A channel of the encoder 12. Similarly, PWM
signal OFFSETB_PWM output by the offsetB PWM module 36 controls the
dc offset applied to the signal output by the photo sensor
associated with the B channel of the encoder 12.
As used herein the term "printer" is intended to encompass any
device which is capable of placing indicia on a media, regardless
of the type of print technology and printer mechanism used.
Further, the term "printer" specifically encompasses both stand
alone units and multi-function devices incorporating the capability
of placing indicia on a media (e.g., devices commonly referred to
as combination fax/printers).
Generally it is desirable that the A and B analog encoder signals
of an encoder system such as that of FIG. 1 be produced with the
same amplitude and in the same range. However, variances between
electrical components and mechanical imperfections tend to cause
the signals produced by the photo sensors 16 to differ in amplitude
and range. In the encoder system 10 two primary parameters can be
adjusted in attempt to control the A and B encoder signals
produced, namely the energization level of the light element as set
by the LED_PWM signal and the dc offset of the A and B channels as
set by the OFFSETA_PWM and OFFSETB_PWM signals respectively.
Adjusting light source energization tends to primarily vary the
amplitude of the encoder signals produced while adjusting the dc
offsets tends to primarily vary the range within which the encoder
signals are produced, and that range is considered as being defined
by an upper envelope and a lower envelope, where the upper envelope
is tracks the maximum value of an encoder signal and the lower
envelope is tracks the minimum value of the encoder signal.
The A/D converter 24 has a limited detection range defined by a
maximum and a minimum. In one example, the A/D converter is an 8
bit converter with a detection range having a minimum of zero volts
and a maximum of 3.5 volts. In such a case, the A/D converter
outputs a digital value of zero ("00000000") for any analog input
voltage that is at or below zero volts. Likewise, the A/D converter
24 outputs a digital value of 255 ("11111111") for any analog input
voltage that is at or above 3.5 volts. It has been determined that,
in actual operation, robust performance of the encoder system can
be achieved over a large range of speeds and environments by
utilizing encoder signals that actually extend outside the
detection range of the A/D converter, meaning an upper envelope of
each encoder signal is at an amplitude above the maximum of the
detection range and a lower envelope of each encoder signal is
below the minimum of the detection range. The following procedure
allows the encoder system to be initialized in a simple, effective
manner to achieve such an encoder signal arrangement.
Referring to FIGS. 1-3, one embodiment of an initialization method
is described. Upon beginning the initialization procedure at step
100 the initialization module 28 effects energization of the
printer structure motor at a MOTOR_PWM known to be sufficient to
move the moveable part of the encoder. It is assumed that this
setting remains constant throughout the following steps. At step
102 the initialization module 28 sets up the encoder signals for
measurement by setting the energization level of the light element
14 at a first energization level corresponding to a duty cycle of
LED 1 and likewise sets the channel A offset circuitry to a first
level corresponding to a duty cycle of OFFSETA1 and the channel B
offset circuitry to a first level corresponding to a duty cycle of
OFFSETB1. OFFSETA1 and OFFSETB1 may be the same or different. An
exemplary upper and lower envelope defining only one of the encoder
signals at such settings is shown in region 50 of FIG. 3, with the
understanding that the other encoder signal would have a similar,
though not necessarily identically positioned and sized, envelope.
Portions of an exemplary analog output signal, varying between the
upper envelope and lower envelope, are shown at various positions
in FIG. 3. Both encoder signals will desirably be entirely within
the detection range of the A/D converter. In the illustrated
embodiment, the amplitude defined between the upper envelope and
lower envelope increases as the energization level of the light
element 14 increases. At step 104 the maximum and minimum values of
the encoder signals as output by the MIN/MAX detection hardware 26
are recorded as MAXA1, M1NA1, MAXB1 and MINB1 respectively, and the
LED1 duty cycle setting is also recorded.
At step 106 the initialization module 28 sets up the encoder
signals for a second measurement by setting the energization level
of the light element 14 at a second energization level
corresponding to a duty cycle of LED2 and likewise sets the channel
A offset circuitry to a second level corresponding to a duty cycle
of OFFSETA2 and the channel B offset circuitry to a second level
corresponding to a duty cycle of OFFSETB2. OFFSETA2 and OFFSETB2
may be the same or different.
In one embodiment corresponding to the exemplary equations set
forth below, OFFSETA1=OFFSETA2 and OFFSETB1=OFFSETB2. An exemplary
upper and lower envelope defining the one illustrated encoder
signal after set up for the second measurement is shown in region
52 of FIG. 3. Again, both encoder signals will desirably be
entirely within the detection range of the A/D converter.
At step 108 the maximum and minimum values of the encoder signals
as output by the MIN/MAX detection hardware 26 are recorded as
MAXA2, MINA2, MAXB2 and MINB2 respectively, and the LED2 duty cycle
setting is also recorded. At step 110 the operating energization
level for the light element 14 and the operating levels for the
offset circuitry of each channel are defined by calculating duty
cycle values LEDOP, OFFSETAOP and OFFSETBOP. In one embodiment,
corresponding to OFFSETA1=OFFSETA2 and OFFSETB1=OFFSETB2, the
calculation produces adjustment values for the energization level
of the light element and for the channel A and B offsets according
to the following equations: ##EQU1##
where,
the value 280 in Equation (1) represents the desired peak-to-peak
amplitude for the encoder signals during operation, notably 110% of
the peak-to-peak amplitude of the detection range of the A/D
converter,
the value 128 in Equations (2) and (3) represents the desired
midpoint for each of the encoder output signals, notably centered
in the detection range of the A/D converter;
the value 6 in Equations (2) and (3) is a conversion factor that is
set based upon known characteristics of the amplification and
offset circuitry;
"GX2" is the smaller of either the channel A signal peak-to-peak
amplitude (MAXA2-MINA2) and the channel B signal peak to peak
amplitude (MAXB2-MINB2) during the second measurement step;
"GX1" is the peak-to-peak amplitude, either (MAXA1-MINA1) or
(MAXB1-MINB1), of the channel signal that defines GX2;
"MidA2" is the midpoint of the channel A signal as determined from
MAXA2 and MINA2;
"MidB2" is the midpoint of the channel B signal as determined from
MAXB2 and MINB2;
"MidA1" is the midpoint of the channel A signal as determined from
MAXA1 and MINA1; and
"MidB1" is the midpoint of the channel B signal as determined from
MAXB1 and MINB1.
In the illustrated embodiment, all of the values GX1, GX2, MidA1,
MidA2, MidB1 and MidB2 will be values between 0 and 255. The
operating duty cycle values LEDOP, OFFSETAOP and OFFSETBOP are then
calculated as follows:
Notably, using the value 280 in Equation (1), and producing signals
centered about the detection range, the upper envelope of each
signal will be placed above maximum of the detection range by about
5% of the total amplitude of the detection range and the lower
envelope of each signal will be placed below the minimum of the
detection range by about 5% of such total amplitude. Of course,
values other than 280 could be used in connection with Equation (1)
to vary the position of the upper and lower signal envelopes.
It is recognized that the foregoing equations are exemplary only,
and that other calculation operations could also be implemented to
achieve the desired operating settings for the light element 14 and
the offset circuitry of each channel of the encoder system. The
basic concept is that by measuring a given encoder signal when set
at two different known test settings, the measured values can be
used to linearly interpolate, or otherwise calculate or define, the
necessary operating settings to produce a desired encoder signal
that is saturated outside the detection range of an A/D converter
or other analog signal detector. Regardless of the calculation
operations utilized, as shown for one signal in region 54 of FIG.
3, the result is that the upper envelope of each encoder output
signal at a known operating position above the maximum of the A/D
converter detection range and the lower envelope of each encoder
output signal at a known operating position below the minimum of
the A/D converter detection range. Additionally, the operating
settings for the offset circuitry of each channel desirably result
in the centering of each encoder signal about the A/D converter
detection range.
The foregoing initialization procedure may be implemented at
various times during the life of a printer. For example, each time
the printer is turned on the initialization procedure may be
carried out. Alternatively, or in addition to such times, the
initialization module or control unit may implement the
initialization procedure based upon detection of some ambient
printer condition. In one example the printer may include a
temperature sensor (not shown) and the ambient printer condition
may be a temperature condition, such as one of (i) a detected
temperature change of at least a certain amount since last
initialization or (ii) a detected temperature exceeding a
predetermined temperature.
While the foregoing example of FIGS. 2 and 3 assumes that in both
of measuring steps 104 and 108 both analog output signals of the
encoder are entirely within the detection range of the A/D
converter, it is recognized that in another embodiment the upper
and lower envelope of the signals could be outside the detection
range during one or more of the measurement steps. In such cases,
the initialization module 26 could identify the upper and lower
crossover levels of the A and B channel signals (i.e., the level at
which the two signals repeatedly cross each other) during each of
steps 104 and 108, and utilize those levels when calculating the
operating settings for the light element 14 and the offset
circuitry.
In certain cases it may be desirable to define and utilize
operating settings for the light element 14 and offset circuitry
that will place the upper crossover level of the A and B channel
signals within the detection range and near the maximum of the
detection range and that will place the lower crossover level of
the A and B channel signals within the detection range and near the
minimum of the detection range.
Turning now to FIGS. 4-7, another encoder system 70 and related
initialization procedure will be described. Like components between
encoder system 70 and encoder system 10 of FIG. 1 are numbered the
same. One notable distinction of encoder system 70 is that, rather
than providing the A and B channel encoder output signals to an A/D
converter, the signals are provided as inputs to Schmitt Trigger
Detection circuitry 72. Accordingly, encoder system 70 does not
convert the analog signal levels of the A and B channel encoder
signals into corresponding digital values. Instead, the Schmitt
trigger detection circuitry 70 defines an upper threshold level and
a lower threshold level for each of the encoder signals and outputs
signals indicating when those levels are crossed by the respective
signals. Referring to one embodiment of the Schmitt Trigger
detection circuitry as shown in FIG. 5, an A channel Schmitt
Trigger 74 and B channel Schmitt Trigger 76 are provided. Ideally,
the Schmitt Triggers 74 and 76 are identical, with similar upper
and lower threshold levels. The output of Schmitt Trigger 74 is
connected to a latch circuit 78 and, through a NOT gate, to latch
circuit 80. Similarly, the output of Schmitt Trigger 76 is
connected to a latch circuit 82 and, through a NOT gate, to latch
circuit 84. The outputs HTA, LTA, HTB and LTB of the respective
latches indicate when the particular thresholds are reached. The
latch circuits 78, 80, 82 and 84 can be reset via the illustrated
reset line R.
Referring now to the flow chart set forth in FIGS. 6A-6D, an
encoder initialization process is described. The process starts at
step 200 and at step 202 the initialization module 28 sets the duty
cycle of the LED_PWM signal to zero, sets the duty cycle of each of
the offset PWM signals to zero and sets the duty cycle of the
MOTOR_PWM signal to a value known to produce movement, in this
example 20%. After a small delay at step 204, the latching circuits
are reset at step 206. Then, per steps 208, 210, 212, 214, 216, 218
and 220, the duty cycles, OffsetA and OffsetB, of both offset PWM
signals are increased until both the A channel encoder signal and
the B channel encoder signal reach the upper threshold level of
their respective Schmitt Triggers as indicated by HTA and HTB going
high. This process is shown for a single encoder channel in region
80 of the graph of FIG. 7. Notably, because the light element is
not energized during theses steps, the encoder signal appears as a
solid line, rather than having an upper and lower envelope. The
offset duty cycles corresponding to the upper threshold level for
each channel are then recorded as OffzHlA and OffzHB respectively
at step 222.
Next, in steps 224, 226 and 228 the duty cycles, OffsetA and
OffsetB, of the offset PWM signal of both channels are set to 100%
momentarily and the latching circuits associated with the Schmitt
Triggers are reset, which is shown graphically for a single signal
in region 82 of FIG. 7. At step 230 the offset duty cycles are set
back to the OffzHA and OffzHB values. In steps 232, 234, 236, 238,
240, 242 and 244, the duty cycles, OffsetA and OffsetB, of the
offset PWM signals of the two channels are decreased until both the
A channel encoder signal and the B channel encoder signal reach the
lower threshold level of their respective Schmitt Triggers as
indicated by LTA and LTB going high. This process is shown for a
single signal in region 84 of FIG. 7. At step 246 the duty cycles
corresponding to the lower threshold level for each channel are
then recorded as OffzLA and OffzLB. In steps 248, 250 and 252 the
duty cycles, OffsetA and OffsetB, of both channels are set to 100%
and the latching circuits associated with the Schmitt Triggers are
reset, which is shown graphically for a single signal in region 86
of FIG. 7.
In steps 254, 256 and 258 the duty cycle LED of the LED_PWM signal
is then incrementally increased until the lower envelope of the A
channel encoder signal or the lower envelope of the B channel
encoder signal reaches the lower threshold level of the respective
Schmitt Trigger as indicated by LTA or LTB going high, and shown
graphically for a single signal in region 88 of FIG. 7. At step 260
the duty cycle just below that which caused a lower threshold to be
reached is recorded as LEDE, and in steps 262, 264 and 266 the
latching circuits associated with the Schmitt Triggers are reset
while the duty cycle of the LED_PWM signal is zero, which is
illustrated in region 90 of FIG. 7. At step 268 the duty cycle LED
of the LED_PWM signal is reset to the LEDE value and then in steps
270,272, 274, 276, 278, 280 and 282 of FIG. 6B the duty cycles,
OffsetA and OffsetB, of both offset PWM signals are repeatedly
decreased until the lower envelope of each of the A channel encoder
signal and the B channel encoder signal reaches the lower threshold
level of the respective Schmitt Triggers as indicated by LTA and
LTB going high, which is shown graphically for a single signal in
region 92 of FIG. 7. At step 284, the offset duty cycles
corresponding to the lower threshold for each channel are recorded
as OffLTA and OffLTB.
In step 286 the duty cycles for the offset PWM signals are set low,
back to the OffzHA and OffzHB values, and the latching circuits are
reset per steps 288 and 290. In steps 292, 294, 296, 298, 300, 302
and 304 the duty cycles of both offset PWM signals are repeatedly
increased until the upper envelope of each of the A channel encoder
signal and the B channel encoder signal reaches the upper threshold
level of the respective Schmitt Trigger as indicated by HTA and HTB
going high, which is shown graphically for a single signal in
region 94 of FIG. 7. The offset duty cycles corresponding to the
upper threshold level for each channel are then recorded as OffHTA
and OffHTB respectively at step 306.
In step 308, the peak to peak amplitude (GA) of the A channel
encoder signal and the peak to peak amplitude (GB) of the B channel
encoder signal are calculated per the exemplary equations.
Referring to the equation for GA, the value (OffzHA-OffzLA)
represents the range between the Schmitt trigger's upper and lower
thresholds, the value (OffLTA-OffHTA) is the difference between the
duty cycle of the OffsetA_PWM signal that trips the lower threshold
and the duty cycle of the OffsetA_PWM signal that trips the upper
threshold, and the number 6 is a known conversion factor particular
to the characteristics of the amplifier and offset correction
circuitry, and therefore could vary depending upon the
characteristics of such circuitry in any given system. Thus, the
exemplary equations find the peak to peak amplitude of the encoder
signals by summing the portion of each of the encoder signals that
is beyond the Schmitt trigger hysteresis range with the hysteresis
range. In step 310 the duty cycle, OffsetA and OffsetB, of each of
the offset PWM signals is set to a value that centers its
respective encoder signal about the upper and lower threshold
levels, which is shown graphically in region 96 of FIG. 7.
In steps 312, 314 and 316 if the peak to peak amplitude of either
of the channels is below a certain value, in this example 320,
which is 125% of 256 (the size of the detection range of the A/D
converter in the prior embodiment), an adjustment value LEDadj for
the duty cycle of the LED_PWM signal needed to bring the amplitude
up to the certain value is calculated per the illustrated equation.
At step 318 the duty cycles, OffsetA and OffsetB, of the offset PWM
signals are both adjusted per the illustrated equation to again
achieve centering and at step 320 the value LEDadj is added to duty
cycle LED of the LED_PWM signal. The initialization procedure ends
with steps 322 and 324.
The foregoing initialization procedure results in a method for
initializing an analog output signal of an encoder system, without
converting analog signal level to corresponding digital values,
involving the steps of (a) inputting the analog output signal to an
upper level detector that detects when the analog output signal
increases to an upper threshold level; (b) repeatedly adjusting the
setting of the dc offset circuitry to increase the offset of the
analog output signal until the level detector outputs an indicator
that the upper threshold level is reached; (c) recording the
setting of the dc offset circuitry corresponding to the output of
the indicator of step (b); (d) inputting the analog output signal
to a lower level detector that detects when the analog output
signal decreases to a lower threshold level; (e) repeatedly
adjusting the setting of the dc offset circuitry to decrease the
offset of the analog output signal until the lower level detector
outputs an indicator that the lower threshold level is reached; (f)
recording the setting of the dc offset circuitry corresponding to
output of the indicator of step (e); (g) placing the setting of the
dc offset circuitry at a level to produce a high dc offset and
repeatedly adjusting the energization level of the light element to
increase an envelope of the analog output signal until the lower
level detector outputs an indicator that the lower threshold level
is reached; (h) subsequent to step (g), adjusting the energization
level of the light element to place the envelope of the analog
output signal above the lower threshold level and: (i) adjusting
the setting of the de offset circuitry to decrease the offset of
the envelope until the level detector outputs an indicator that the
lower threshold level is reached, (ii) recording the setting of the
dc offset circuitry corresponding to output of the indicator of
(h)(i); (i) subsequent to step (h), placing the setting of the dc
offset circuitry at a level to produce a low dc offset and: (i)
adjusting the setting of the dc offset circuitry to increase the
offset of the envelope until the upper level detector outputs an
indicator that the upper threshold level is reached, (ii) recording
the setting of the dc offset circuitry corresponding to output of
the indicator of (i)(i).
In an alternative initialization procedure useful in connection
with the encoder system of FIG. 4, the duty cycle of the LED_PWM
signal and the duty cycles of both offset PWM signals are all set
to zero and the duty cycle of the MOTOR_PWM signal is set to a
non-zero value sufficient to produce movement of the printer
structure 18. The separation between the upper and lower Schmitt
Trigger thresholds is then determined by increasing and decreasing
the duty cycles of the offset PWM signals and monitoring the
outputs of the Schmitt triggers. Next, the duty cycle of the
LED_PWM signal is increased to grow the encoder signal peak to peak
amplitudes to a first level, and then the actual peak to peak
amplitudes values are estimated by increasing and decreasing the
duty cycles of the offset PWM signals and monitoring changes in the
Schmitt Trigger outputs. Next, the LED_PWM is adjusted to set the
encoder signal peak to peak amplitudes at a second level, and then
the actual peak to peak amplitudes are estimated by increasing and
decreasing the duty cycles of the offset PWM signals and monitoring
changes in the Schmitt Trigger outputs. The
measurements/estimations are then used to determine the needed
operating duty cycles for the LED_PWM signal and the offset PWM
signals to give desired encoder output signals.
While FIG. 4 and the related initialization procedures described
above contemplate the use of Schmitt Triggers, it is recognized
that other types of analog signal level detectors that do not
convert analog levels to digital values could also be used. The
foregoing initialization procedures associated with FIG. 4 could be
implemented at various times such as power up and/or based upon
detection of an ambient printer condition as previously
described.
Although the invention has been described above in detail
referencing the illustrated embodiment thereof, it is recognized
that various changes and modifications could be made.
* * * * *